Did 55 miles. I will be 55 in 3 weeks. Averaged 15.6 mph. Did it myself with no stopping. Rolling out and back course. For those of you MotionBased literate the ride can be found here: http://trail.motionbased.com/trail/activity/3382315. Kind of bonked the last 5-10 miles. I hadn't eaten much during the day. I was going to take 2 cliff bars, but I forgot to. I could have used them. I did drink about 70-80 oz of dilute gatorade during the ride. My legs really ached the last few miles (tho I din't really slow up) and hurt for a while after. Feel OK now. I think with more food, I would have been ok.
My brother in law who is 62 or 63 is in the middle of this: http://www.redspoke.org/. 300 miles in 5 days across Washington state.